It is important to prevent leakage of injection molding material, be it plastic melt, molten metal, thermoset material, or some other material. The safety and integrity of injection molding operations depend on leak-proof or leak-resistant sealing of runners.
In many conventional designs, sealing at the interface between runner components, such as a hot runner manifold and the head of a connected nozzle, becomes weaker as the molding material pressure increases. Such a seal may eventually fail because of cyclic loading due to discrete injection molding “shots.” It may fail for other reasons instead.
To maintain a good seal between runner components, the amount of preload on these components can be critical. In the case of hot-runner components, an air gap between these components is often required during cold conditions to achieve a good seal during higher, operating temperatures, after the components have undergone thermal expansion. If the true operating temperature is different from the designed operating temperature, the seal may not be effective. By the same token, as the system is heated to operating temperature, the air gap takes time to close.
High manufacturing tolerances may also be required to ensure a good seal.
Conventional solutions include using Belleville washers to create a preload between the flange surface and the manifold surface, using a sealing bushing of different material to create a seal due to differential heat expansion, using the heat expansion of the manifold and the flange to create a strong seal by limiting the air gap between the manifold plate and the top clamping plate, and using runner components that are threaded together.
U.S. Pat. No. 6,561,790 to Blais et al., which is incorporated by reference in its entirety herein, discloses a sealing member located between two manifolds, amongst other things. The sealing member concentrates sealing pressure adjacent the melt channels. An array of seal geometries are proposed, but suitable materials are not disclosed. Blais et al. suggest relying on thermal expansion and a spring means to achieve the seal.
US Published Patent App. No. 2003/0075563 in the name of Bazzo et al., which is incorporated by reference in its entirety herein, discloses a seal in the form of a substantially hemispherical annular member that ensures sealing even when an angle exists between nozzle and manifold. The hemispherical annular member acts as a ball-joint. Although it is disclosed that the sealing effect is further enhanced by the action of the pressure of the fluid plastic material applied against the inner wall of the substantially hemispherical annular member, the extolled hemispherical shape hinders the action of the pressure, which reduces the effectiveness of the seal.